What is 21/63 + 4/8?

Here's how you add

Step 1

We can't add two fractions with different denominators (the bottom number). So you need to get a common denominator - both bottom numbers need to match. To do this, you'll multiply the denominators times each other... but the numerators have to change, too. They get multiplied by the other term's denominator.

So we multiply 21 by 8, and get 168, then we multiply 63 by 8 and get 504.

Do the same for the second term. We multiply 4 by 63, and get 252, then multiply 63 by 8 and get 504.

So now our fractions look like this:

Step 2

Since our denominators match, we can add the numerators.

168 + 252 = 420

So the answer is:

Step 3

Last of all, we need to simplify the fraction, if possible. Can it be reduced to a simpler fraction?

To find out, we try dividing it by 2...

Are both the numerator and the denominator evenly divisible by 2? Yes! So we reduce it:

Let's try dividing by that again...

Are both the numerator and the denominator evenly divisible by 2? Yes! So we reduce it:

Let's try dividing by that again...

Nope! So now we try the next greatest prime number, 3...

Are both the numerator and the denominator evenly divisible by 3? Yes! So we reduce it:

Let's try dividing by that again...

Nope! So now we try the next greatest prime number, 5...

Nope! So now we try the next greatest prime number, 7...

Are both the numerator and the denominator evenly divisible by 7? Yes! So we reduce it:

Let's try dividing by that again...

No good. 7 is larger than 5. So we're done reducing.

There you have it! Here's the final answer to 21/63 + 4/8